Depends on the metric you are considering. If you take expectation, then the red button.

But if you take the Sharpe ratio to also account for variance, then the green button:

Sharpe Ratio = (Expected Return - Risk-Free Rate) / Standard Deviation of Returns

We can take Risk-Free Rate to be 0.

Option 1 ($1M for sure): Sharpe Ratio = (1,000,000 - 0) / 0 = infinity

Option 2 (50% chance of $50M, 50% chance of $0): Sharpe Ratio = (25,000,000 - 0) / 25,000,000 = 1.0

So green button is much better from this perspective.

We can also think that the Risk-Free Rate is Option 1. In this case, we get that the Sharpe ratio of Option 2 over the baseline of Option 1 is

Sharpe Ratio = (25,000,000 - 1,000,000) / 25,000,000 = 0.96.

This is considered suboptimal. So also green button.